Various types of communicating device for transmitting and receiving signals among plural vehicles in order to exchange information have been known so far, and, for example, an inter-vehicle communication system disclosed in JP2001-283381A is capable of communicating information among plural vehicles traveling on a road. The inter-vehicle communication system includes a drive aiding camera mounted on the user's vehicle itself in order to support driving and captures images around the user's vehicle. On the basis of the captured images, traveling related information including a traffic condition around the user's vehicle is detected, and the information is transmitted to the other vehicles by means of a wireless transmitter.
Further, as a technology for general mobile communications, a Multi-hop Wireless Network has been known so far. For example, by means of the Multi-hop Wireless Network, signals can be relayed among movable bodies so that the movable bodies, which cannot directly communicate each other, can indirectly communicate each other. Further, a routing protocol used for building routes of various kinds of Multi-hop Wireless Networks has been developed.
According to the device disclosed in JP2001-283381A, when the user's vehicle detects a traffic condition or abnormal occurrences, it sends the information to all vehicles, which exist within a range where a wireless communication is available. However, because the wireless communication generally uses signals of a high frequency wave, when obstacles such as a building exist between the vehicles, it becomes difficult to communicate between vehicles behind the obstacles.
Further, even when the signals are blocked by a building or the like and cannot be sent and received between two vehicles, using the routing protocol used for building routes of various kinds of Multi-hop Wireless Networks, the signals are relayed by another movable body and appropriately sent and received between the two movable bodies. However, within the Multi-hop Wireless Network between movable bodies such as vehicles, because the signals are randomly hopped, it takes some time to converge the route and communication efficiency is decreased
A need thus exists to provide a communication device for a movable body mounted to each of movable bodies for exchanging information among the movable bodies that can, even when an obstacle exists between movable bodies, a signal is relayed by a movable body, which is positioned at appropriate area (e.g. obstacle-free area) and selected to relay the signal, in order to sent and receive the signal appropriately between movable bodies.